A transparent solution was obtained by treating silk fibroin with dichloroacetic acid for one day at room temperature. The 1% solution gave cloudy precipitates by diluting with the same volume of water.Needle-shaped crystals could be observed under optical microscope in the precipitates dried up on a slide glass at about 60°C.The particles have sizes within the range of 0.5 to 5μ in width and 100 to 300μ in length.Similar particles were also observed in the concentrated solution heated to 60°C. Fibrillar precipitates were obtained in more concentrated solution.X-ray powder diagram of the fibrillar materials indicated presense of crystals with the extended β-configuration.The fibroin film made from dichloroacetic acid solution were also identified as having the β-configuration by infrared absorption spectra showing the amide 1 band at 1625cm-1 and the amide II band at 1520cm-1.The result of electron diffraction coincided with those obtained by other methods.